For Direct Sequence Code Division Multiple Access (DS-CDMA) location systems, the transmitter may be turned on only several times per day, and may broadcast only a few frames of data. Additionally, the frame may be very short (200 bits per frame for example). Consequently, the transmitter is quiet for most of the time. However, in order to avoid missing any signal, a typical receiver will continuously perform a real-time correlation between a known pseudo-noise (PN) sequence and the input signal, as if a signal transmission were present. From the results of the correlation, a determination is made as to whether or not a signal is present, and whether the signal should be processed further. The correlation process constitutes a large proportion of the total processing required to demodulate and extract the data from the input signal. Thus, a great deal of processing is being done, even if no signal is present.
The correlation process requires a large amount of processing power in this type of receiver configuration, and must be performed in real-time. Consequently, the processing is typically performed using specialized hardware rather than a general purpose digital signal processor (DSP).
For a “burst” application, such as that in a location system, real-time processing to demodulate and extract the data is not required, provided that the incoming data can be stored for later processing. The amount of incoming data is very large, so it is preferable that signal detection is performed so as to identify which portions of the incoming system should be stored.
There is therefore a need in the art for a signal detection system that can operate in real-time with a reduced processing requirement.
Further, if the signal detection and data demodulation/extraction can be performed in software on a DSP, a simpler, lower cost receiver can be designed.